The present disclosure relates to hydraulic control systems, and especially to seal members and seal assemblies used in a master cylinder of a hydraulic braking system.
Conventionally, a master cylinder for developing fluid pressure according to pedal force applied by a brake or clutch pedal is used in a hydraulic brake or clutch system for the purpose of actuating a brake or a clutch. A typical master cylinder for a hydraulic braking system 10, as generally depicted in FIG. 1, comprises a master cylinder 12 fed by a brake fluid reservoir 14. The master cylinder includes a primary cylinder body 16 and a secondary cylinder body 18 in communication through a common cylinder bore 22. A primary piston 20 is slidably disposed within the cylinder bore 22.
The master cylinder includes sealing members between the cylinder bore 22 and the primary piston 20 (as well as the secondary piston disposed in the secondary cylinder body 18). In some master cylinders, the sealing members are mounted within the cylinder body, with the pistons traversing an inner surface of the sealing members. One such exemplary seal configuration is shown in U.S. Pat. No. 7,520,132, assigned to Bosch Corporation, which issued on Apr. 21, 2009, the disclosure of which is incorporated herein by reference.
In another seal configuration, the primary piston 20 includes a number of sealing members 24, 25 received in corresponding grooves 26, 27 formed in the body of the piston, as depicted in FIG. 1. In this configuration, the sealing members 24, 25 move with the piston within the cylinder bore 22. The seal configuration includes a glide ring formed of TEFLON®.
In a hydraulic control system, and especially in a braking system, it is essential to maintain the pressures within the master cylinder and to avoid leakage around the piston(s) in the system. At the same time, the pistons must be capable of relatively free sliding within the cylinder bore to ensure suitable responsiveness of the hydraulic system and to maintain an appropriate activation pressure, particularly for an automotive braking system. There is always a need for a sealing arrangement that is capable of proper sealing at low and high pressures without introducing unnecessary drag to the sliding action of the pistons within the hydraulic cylinder.